array.ts

Object.defineProperties(Array.prototype, {
  where: { value: Array.prototype.filter },
  select: { value: Array.prototype.map },
  any: { value: Array.prototype.some },
  all: { value: Array.prototype.every },
  insert: { value: function (position: number, items: Array<any>) { return (<Array<any>>this).splice(position, 0, ...items); } },
  selectMany: { value: function (callbackfn: (value: any, index: number, array: Array<any>) => Array<any>) { return (<Array<any>>this).select(callbackfn).flat(); } },
  groupByMap: { value: function (keySelector: (each: any) => any, selector: (each: any) => any) { 
    const result = new Map<any, Array<any>>();
    for (const each of this) {
      const key = keySelector(each);
      if (!result.has(key)) {
        result.set(key, new Array<any>());
      }
      result.get(key)!.push(selector(each));
    }
    return result;
  }},
  groupBy: {
    value: function (keySelector: (each: any) => any, selector: (each: any) => any) {
      const result = <any>{};
      for (const each of this) {
        const key = keySelector(each);
        (result[key] = result[key] || new Array<any>()).push( selector(each));
      }
      return result;
    }
  },

});

declare global {
  interface Array<T> {
    where: typeof Array.prototype.filter;
    select: typeof Array.prototype.map;
    any: typeof Array.prototype.some;
    all: typeof Array.prototype.every;
    /**
       * Removes elements from an array and, if necessary, inserts new elements in their place, returning the deleted elements.
       * @param start The zero-based location in the array from which to start removing elements.
       * @param deleteCount The number of elements to remove.
       * @param items Elements to insert into the array in place of the deleted elements.
       */
    insert(start: number, ...items: Array<T>): Array<T>;
    /**
      * Removes elements from an array returning the deleted elements.
      * @param start The zero-based location in the array from which to start removing elements.
      * @param deleteCount The number of elements to remove.
      */
    remove(start: number, deleteCount?: number): Array<T>;

    selectMany<U>(callbackfn: (value: T, index: number, array: Array<T>) => U): Array<U extends ReadonlyArray<infer InnerArr> ? InnerArr : U>;
    groupByMap<TKey,TValue>(keySelector: (each: T) => TKey, selector: (each: T) => TValue): Map<TKey, Array<TValue>>;
    groupBy<TValue>(keySelector: (each: T) => string, selector: (each: T) => TValue): { [s: string]: Array<TValue> };
  }
}